Jet-driven helicopter rotor



Jan. 26, 1954 F. L. DOBLHOFF JET-DRIVEN HELICOPTER ROTOR Filed April 9. 1947 Patented Jan. 26, 1954 JET-DRIVEN HELICOPTER ROTOR Friedrich List Doblhofl, Zell am See, Austria, as- Signor to The Fairey Aviation Company Limited, Hayes, England Application April 9, 1947, Serial No. 740,366

Claims priority, application France May 18, 1946 8 Claims.

This invention relates to improvements in reaction propulsion particularly adapted for use with helicopters, but also useful with ordinary aircraft.

It is known that the use of reaction propulsion in helicopters permits the avoidance of the couple which occurs with the mechanical drive of the rotors, and the avoidance of the need for anticouple devices such as tail propellers and double rotors. Reaction propulsion also does away with the weight, the costs of construction, and the maintenance of reciprocating motors, and greatly reduces the number of mechanical elements involved.

- It is known to use reaction propulsion which utilizes a compressor driven by a turbine. Such devices utilize a portion of the pressure furnished by the compressor and a portion of the energy produced by combustion chambers located between the turbine and the compressor, the eX- haust gases of the turbine being conducted through the hub of the rotor and through a system of pipes through the blades to jets situated at the extremity of the blades where the gases are finally expelled and furnish the reaction which produces the desired rotation of the rotor blades. These known propulsion devices present numerous serious inconveniences.

The turbine necessitates quite a high temperature in order to operate well. The obtaining of such a high temperature is difiicult for the following reasons: Because of the high temperature and of the low pressure, the specific volume of the exhaust gas is so large that the blades of the helicopter need to be much larger than can operate at maximum aerodynamic efliciency, and particularly if one takes into consideration the fact that reaction propulsion necessitates high linear speeds at the extremity of the blades.

Another difiiculty is involved in constructing the rotor hub with its conduits and its articulated joints conducting the gas in the blades in a manner so that it can function at high temperature. The same difliculty is present with the blades.

Another trouble is the considerable waste of energy due to the cooling of the gases caused by the large surfaces of the blades.

Certain of these difficulties do not exist where the turbines or combustion chambers are disposed in the extremities of. the blades, but such dispositions give rise to serious gyroscopic problems as well as weight problems involving the inertia of theblades.

An object of the invention is to provide a. jet

or nozzle cross-sectional area which can be varied as the speed of the tip of the blade varies.

This permits power control by merely changing the pitch of the blades as the rotational speed of the rotor would therefore automatically remain practically constant.

The control of the cross-sectional area of the nozzle can be accomplished by utilizing centrifugal force, in which case the rotational speed of the rotor would remain constant. Control can also be accomplished by utilizing the dynamic pressure of the atmospheric air, in which case the speed of revolution of the rotor would depend upon the rotor tip speed and the density of the air. In thinner air (higher altitudes) the speed of revolution of the rotor would automatically increase, thus compensating for the loss in lift which would occur if the aircraft continued ascending into the thinner atmosphere without any variation in the speed or pitch of the blade.

When the cross-sectional area of the jets or nozzles is increased, a greater amount of air will flow therethrough. This necessitates the compressors being driven with greater power. This can be accomplished by an automatic device which maintains the turbines R. P. M. and therefore the compressor R. P. M. fairly constant by varying the fuel pressure in the fuel line leading to the combustion chambers, or by adjusting the position of the stator blades of the turbine.

The above and other objects of the invention will be apparent from the following specification and the accompanying drawings, in which:

Fig. l is a perspective view, partially schematic, of the tip of a helicopter rotor blade showing a device operating in response to centrifugal force for controlling the cross sectional area of the jet nozzle at the end of the blade;

Fig. 2 is a View similar to Fig. 1 but showing a device operating in response to atmospheric pressure of the air in which the rotor is operating.

An important part of the invention is the automatic control of the cross sectional area of the jet nozzles at the ends of the rotor blades. As shown in Fig. l a rotor blade 40 has in its interior a plurality of hot air conducting tubes 4| which are bent at the end of the blade 40 in the direction of the trailing edge of the blade so that their open ends 42 direct the hot air under pressure in such manner as to cause rotation of the blades about the central axis of the rotor. The area of the open ends 42 of tubes 4| may be controlled by a pair of shutters 43 mounted on parallel shafts and extending along the upper and lower edges of the openings 42. Both of the shutters 43 are connected by linkage 44 to one end of a bell crank lever 45 pivoting about a vertical axis, the other end of lever 45 carrying a weight 46. A spring 41 is attached to lever 45 at the end bearing weight 46 in such a manner as to urge'that'end of the lever inwardly toward the axis of rotation of the rotor blade 40, thereby tending to retain shutters 43 in their wide open positions.

When the rotor of the helicopter is rotating, centrifugal force will act on weight t6 'in'opposition to the pull of spring'l so'that the ,higher the speed of rotation of the rotor, the further outwardly will move weight 46, causing shutters 43 to move toward each other. This of course results in a decrease in the cross sectional area of the openings 42 with a correspondingjlessening of the thrust and a decrease in the speed of rotation of the rotor. As the rotational speed decreases, the centrifugal force acting on weight 47 also decreases and spring will cause move ment of shutters as to more open positions. I In this manner automatic control of the speed of rotation of the blades may be achieved.

In order to avoid hunting (too rapid oscillation of weight 45) there is provided a buffing or movement retarding device 48 connected to bell crank lever 45 so as to exert a steadying effect thereon.

When shutters A3 are open to increase the active cross sectional area of openings .42, it is necessary for the compressor 2:3 to furnish a greater mass of .fiuid, and consequently the turbine must be driven with greater power. This can be accomplished by an automatic device which maintains the speed of rotation of the turbine, and therefore'of the compressor, fairly constant. Such a device could operate, for example, from the pressure of an oilpump driven by the shaft 30 of the turbine for supplying lubrication to the shaft bearings, or could be accom-, plished by a centrifugal governor driven by shaft 38. The chosen regulating device, oil pressure or centrifugal force, canbe connected tocontroi thesupply of fuel to burnersZfi, orto change the pitch of the blades of the stator of :the turbine.

As shown in Fig. 2, the variation-of thecross sectional area of openings 42 at the endof blades 48 can be controlled in response toia'ir pressure. In such'an'installation,the shutters 43 are connected as in Fig. 2 by alinkage d' l to a bell crank lever 45. However in thiscase, the-,Qtherendof the bell crank lever is -connectedby a rod 353 to a piston 53 within a cylinderefi. AEitottube 153 having its open end 5 facing in the direction of rotation of the blade is connected to cylinder 52 in such manner that the airpressure vin tube 53 controls the position of piston -5l in cylinder 52 and thereby controls thepositions oil'shutters 4.3. If desired, a spring (not shown) maybe mountedin opposition to the efiect vof-the pressure'in cylinder-52 ,on the position of the shutters.

It will be apparent that the pressure in tube 53iis a function of the speed of rotationof .the rotor blades and of the density of theair, so that as the aircraft-rises to higher altitudes and the air becomes thinner, shutters-t3 will be opened wider to give a greater thrust and therebyto increase the speed of .rotation'of the rotor.

I wish it to be understood thatthe constructionlhave described'herein is shown only'in an exemplary sense and is.11ot tobe construed as the only manner of carrying'out myinvention. It'is my.intention to cover allrmodificationsffall- ;z le in said blade in communication with said internal passage for expelling said heated fluid to cause rotation of said blades, closure means cooperating with said nozzle for varying the effectiveLcrosssectional area of the opening of said nozzle, and control means connected to said closure means and substantially operable in response to the speed of rotation of the rotor for controlling the :position of said closure means, said control means being operable to move said closure means to decrease the area of the opening of said nozzle when the speed of rotation of the rotor increases beyond a predetermined value,

and to move said closure means to increase thenozzle area when the speed of rotation of the rotor decreases below said value.

2. A reaction propulsion device for helicopters as set forth in claim '1, said control means comprising a weight, means mounting said weight to said blade for movement away from therotor axis by centrifugal force, resilient means connected to said blade and said weight tending "to resist said movement of the-weight, anda linkage connecting said weight to said closure and operable by said weight for moving said closure means to decrease the cross sectional area of the nozzle opening upon outward movement of said weight in response to an increase in "the rotational speed of the rotor beyond a predetermined value and for moving said closure means to increase the crosssectional area of the nozzle opening upon inward movement of said. weight by saidresilient means in response ;to a decrease in the rotor speed below said value.

3. A reaction propulsion device for helicopters as set forth'in claim 2, anddamper means connected to said linkage to control the speed of operation of said control means.

4. A reactionpropulsion device for-helicopters as set forth inclaim l, said'control means comprising a cylinder, a piston in said cylinder, a linkage connecting said piston with said closure means whereby'the position of said piston controls the effective opening of said nozzle, and a Pitot tube communicating with the interior of said cylinder and open 'to the exterior vof the blade in the. direction of the direction of rotation of the rotor, whereby the air pressure said Pitot tube controls the position of said piston and thereby the position of said closure means as a functionof the speed of rotationof the rotor andthe density of the air in which the rotor is. operating.

.5. Ina rotating helicopter'bladehaving'a re- 1 action nozzlenear its outer end for rotating the blade about a roter'hub, an arrangement for controlling the size of thenozzleopening to control the speed of-rotation -of the rotor, comprising closure :'means mounted adjacent the outlet end of said nozzle, and control ,,means independent of mechanical linkage to said rotor hub and substantially operable in response to the speed of rotation of the rotor for controlling the position of said means connecting said control means to said closure means, said control means being operable to move said closure means v,to diminish the Leif ective -nozzle opening when the speed of rotation of the rotor increases beyond a predetermined value, and to move said closure means to enlarge the effective nozzle opening when th speed of the rotor decreases below said predetermined value.

6. The combination set forth in claim 5, said control means comprising a weight, means mounting said weight to said blade for movement away from the rotor axis by centrifugal force, resilient means connected to said blade and said weight tending to resist said movement of the weight, and a linkage connecting said weight to said closure and operable by said weight for moving said closure means to decrease the cross sectional area of the nozzle opening upon outward movement of said weight in response to an increase in the rotational speed of the rotor beyond a predetermined value and for moving said closure means to increase the cross sectional area of the nozzle opening upon inward movement of said weight by said resilient means in response to a decrease in the rotor speed below said value.

7. The combination set forth in claim 5, said control means comprising a weight, means mounting said Weight to said blade for movement away from the rotor axis by centrifugal force, resilient means connected to said blade and said weight tending to resist said movement of the weight, and a linkage connecting said weight to said closure and operable by said weight for moving said closure means to decrease the cross sectional area of the nozzle opening upon outward movement of said weight in response to an increase in the rotational speed of the rotor beyond a predetermined value and for moving said closure means to increase the cross sectional area of the nozzle opening upon inward movement of said weight by said resilient means in response to a decrease in the rotor speed below said value, and damper means connected to said linkage to control the speed of operation of said control means.

8. The combination set forth in claim 5, said control means comprising a cylinder, a piston in said cylinder, a linkage connecting said piston with said closure means whereby the position oi and the density of the air in which the rotor is operating.

FRIEDRICH LIST DOBLHOFF.

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